Field of the Invention
The present invention relates to an inkjet printing method for printing on at least one curved region on the surface of an object. The invention further relates to a device for implementing the method.
The technical field of the invention is the field of printing on surfaces of three-dimensional objects or bodies. The surfaces may be curved and are printed-on in an inkjet process. For that purpose, a robot arm guides an inkjet print head along the surface to be printed-on at a printing distance.
Many patent applications and patents describing inventions in the technical field indicated above are known from the prior art. The Applicant of the instant application has filed patent applications in that technical field, e.g. German Patent Application DE 10 2012 006 371 A1, corresponding to U.S. Pat. No. 9,266,353; German Patent Application DE 10 2014 011 301 A1, corresponding to U.S. Patent Application Publication US 2015/0062244; and German Patent Application DE 10 2015 205 631 A1. Those patent applications and patents include detailed descriptions of devices and methods for providing any desired printed image to any location on any desired three-dimensional object or rather on any type of curved surface thereof. As indicated above, an inkjet print head guided by a robot is used in the process. Both the robot and the print head are connected to a control unit, i.e. a computer, that is equipped with the required computing programs and data for controlling the movement of the robot and the ejection of ink by the print head in accordance with the printed image.
In contrast to printing on flat substrates such as sheets of paper, a problem with printing on curved surfaces is that the density of the ink droplets that are applied to the surface to be printed-on and the tone values created in that way may be subject to fluctuation. Those fluctuations cause undesirable visible defects in the printed image. Such fluctuations and defects thus need to be avoided.
Japanese Patent Application JP 2011227782 A likewise deals with printing on objects and discloses a method for that purpose. However, that document does not provide information on the aforementioned question of how to avoid undesired tone value fluctuation and the technical measures to be taken to do that.